Nucleate boiling is a very effective heat-transfer mechanism, as it can realize high rates of energy transport with minimal temperature drop across engineering surfaces. Nucleate boiling, however, is limited by the critical value of the heat flux (CHF) at which a transition to a deteriorated boiling mode, called film boiling, occurs. In practical applications of boiling, it is desirable to have a high heat-transfer coefficient, and maintaining the operating heat flux below the CHF is advantageous. A high CHF value is also desirable because, everything else being the same, the allowable power density that can be handled by a device based on nucleate boiling is roughly proportional to the CHF. To a first approximation, a 50% increase of the CHF can, therefore, result in 50% higher power density or, equivalently, 50% more-compact cooling systems for electronic devices, nuclear and chemical reactors, refrigeration systems, boilers, etc., with performance and economic benefits in all these applications.
Ways to increase the boiling heat transfer coefficient and CHF have been explored for decades; approaches include, e.g., surface micro-machining and surface coating to increase the number of bubble nucleation sites or use of surfactants to control surface tension. A recent approach that builds on the opportunities created by the rapid expansion of nanotechnology includes seeding the boiling fluid of choice with nanoparticles. There is ample experimental evidence that the resulting nanoparticle colloidal dispersions (known as nanofluids) affect the boiling heat transfer coefficient and, notably, enhance the CHF.